They cover the material at all levels (though some people may also need the Foundations of Math guide before launching into the main strategy guides). The "general" parts of each guide are sufficient if you want to score up to 650 or so. If you want something above 650, then you will also have to do some or all of the "advanced" parts of each guide. (The higher the score you want, the more advanced material you have to master.)
Please note: I do not use the Private Messaging system! I will not see any PMs that you send to me!!
Stacey Koprince
GMAT Instructor
Director of Online Community
Manhattan GMAT
Contributor to Beat The GMAT!
Learn more about me